Graphene, often described as the wonder material of the 21st century, is a two-dimensional lattice of carbon atoms arranged in a honeycomb structure. It’s the lightest, strongest, and thinnest material known to humankind and boasts exceptional electrical and thermal conductivity. Graphene’s potential to revolutionize numerous industries has fueled extensive research and innovation, making it a focal point of scientific and technological advancement. While the 2010 Nobel Prize in Physics celebrated the groundbreaking experiments of Sir Andre Geim and Sir Kostya Novoselov, who extracted graphene from graphite using the “scotch tape” method, the history and controversy surrounding this remarkable material trace back much further.
Graphene’s intriguing journey begins with its recognition in the 19th century, long before the Nobel Prize entered the picture. English chemist Benjamin Collins Brodie made early observations about the layered nature of thermally reduced graphite oxide in 1859, contributing to the understanding of graphite’s atomic structure. Over the years, graphene research progressed significantly, with pivotal work by P.R. Wallace in 1947, where he predicted its electronic structure and noted the linear dispersion relation.
Fast forward to 1962 when Boehm and his colleagues identified single graphene sheets using transmission electron microscopy (TEM) and X-ray diffraction. The term “graphene” was officially coined in 1987 to describe individual sheets of graphite and was also associated with early descriptions of carbon nanotubes. In the early 1970s, chemists achieved the deposition of carbon in graphene monolayers on various substrates, marking another milestone in the material’s journey.
The turning point came in 2004 when Andre Geim, Konstantin Novoselov, and their collaborators unveiled their groundbreaking work on graphene structures. Their paper described the fabrication, identification, and Atomic Force Microscopy (AFM) characterization of graphene. They ingeniously employed a simple mechanical exfoliation method, akin to using scotch tape, to obtain thin layers of graphite from a graphite crystal and transfer them to a silicon substrate. Their innovative approach allowed for patterning samples with just a few layers of graphene into a Hall bar and connecting electrodes to it.
Yet, the road to recognition and the Nobel Prize was not without its fair share of controversies and disputes. Some scientists questioned the accuracy of the Nobel committee’s reasoning and pointed to factual errors in their published statements. Others argued that the award was premature and believed that the contributions of other scientists in the field should have been acknowledged. Some even highlighted similar or competing achievements predating Geim and Novoselov’s work.
However, it’s crucial to note that the Nobel committee awarded the prize for groundbreaking experiments, not the “discovery” of graphene. Their decision was largely based on the freestanding nature of the graphene produced by Geim and Novoselov, in contrast to the supported and bonded sheets in previous research. In his Nobel Prize lecture, Andre Geim suggested that their 2004 paper marked the first unambiguous isolation of a single atomic layer of carbon, addressing earlier concerns about graphene’s stability and existence in the free state. While some, like Boehm, had reservations about the committee’s decision, they acknowledged the significance of Geim and Novoselov’s electronic measurements on graphene, which yielded unexpected results.
Regardless of its convoluted history and the controversies that surrounded its recognition, graphene remains an immensely fascinating material with the potential to transform industries. Researchers and companies worldwide are diligently working to develop techniques for producing, utilizing, and integrating graphene into everyday products. The journey of graphene, from its early observations in the 19th century to the groundbreaking experiments of Geim and Novoselov, is a testament to the power of scientific inquiry and innovation.
Graphene: A Complete Chemical History
Graphene is a two-dimensional sheet of densely packed carbon atoms arranged in a single layer. Its structure resembles a crystal honeycomb lattice or a chicken wire fence, and it is often considered a large aromatic molecule in the flat polycyclic aromatic hydrocarbon family. It shares its carbon allotropes with materials like graphite, carbon nanotubes, and fullerenes. This blog will delve deeper into the intriguing history of this unique material.
Introduction to Graphene
Graphene is commonly conceptualized as an infinite alternant of polycyclic aromatic hydrocarbons, with the purest form consisting solely of hexagonal cells. The presence of pentagonal and heptagonal squares is considered a defect in graphene. A single pentagonal cell can transform the graphene plane into a cone, and inserting twelve pentagons can give it the shape of a spherical fullerene. Controlled addition of pentagons and heptagons can result in various complex shapes, including carbon nanobuds. Single-walled carbon nanotubes are sometimes referred to as graphene cylinders, with some featuring a half-sphere-shaped graphene cap at each end.
The Historical Perspective
The journey to understanding graphene began with the observation of single layers of graphite, which could only be seen in bulk materials through transmission microscopy, especially in soot obtained through chemical exfoliation. Early attempts to create thin graphite films via mechanical exfoliation, initiated in 1990 and continued into 2004, resulted in sheets comprising 50-100 layers. Although these efforts didn’t yield graphene as we know it today, they generated substantial interest and set the stage for future breakthroughs.
Chemical Discovery of Graphene
In 2004, a research group led by Andre Geim in Manchester achieved an unexpected breakthrough by extracting single-atom-thick crystallites from graphite. This discovery confirmed the existence of true 2D crystals, including graphene, which was previously considered incapable of existing in a flat state.
However, skepticism persisted until 2005 when another group, led by Philip Kim at Columbia University, supported the findings of Geim’s group. Kim’s team published an article in Nature, providing substantial evidence that the graphite layers they obtained exhibited the electronic properties theorized by Wallace almost six decades earlier.
Fabrication Techniques
Graphene can be fabricated using various methods, with chemical vapor deposition (CVD) being one of the most common techniques. In CVD, heated metal foil is exposed to different gases to deposit a layer of carbon on the metal surface. By adjusting gas flow rates, exposure time, and temperature, researchers can control the thickness and uniformity of the graphene grown through CVD. Typically, graphene formed through CVD appears as a patchwork on the metal’s surface, with continuous single-layer areas overlapping in some regions.
The growth of graphene by CVD is followed by a transfer process that moves the graphene from the metal substrate to other substrates for measurement and application. Most methods involve the use of a polymer to facilitate this transfer. Copper is often chosen as the transition metal substrate because of its effectiveness in capturing carbon deposition. The quality of graphene obtained through CVD on copper and other metals depends on factors like carbon solubility and the electronic and crystal structure of the metal.
Conclusion
Graphene’s journey from its historical origins to its present-day status as a groundbreaking material is marked by persistence, innovation, and scientific breakthroughs. Its potential applications span various industries, and as researchers continue to explore its properties and fabrication methods, the impact of graphene on technology and everyday life is set to grow. The story of graphene is a testament to the capacity of human ingenuity and curiosity to unlock the secrets of the universe.
